The invention generally relates to methods for treating a subterranean formation. More specifically, the invention relates to methods useful for creating a fluid diverting barrier in a zone of a subterranean formation. The methods may be useful in hydrocarbon wells and production methods.
When hydrocarbons are produced from wells that penetrate hydrocarbon producing formations, water often accompanies the hydrocarbons, particularly as the wells mature in time. The water can be the result of a water producing zone communicated with the hydrocarbon producing formations or zones by fractures, high permeability streaks and the like, or the water can be caused by a variety of other occurrences which are well known to those skilled in the art, such as water coning, water cresting, bottom water, channeling at the well bore, etc. As used herein, the term “zone” simply refers to a portion of the formation and does not imply a particular geological strata or composition. In addition, in enhanced recovery techniques such as water flooding, aqueous fluid is often injected under pressure into oil-containing subterranean formations by way of one or more injection wells. The flow of the aqueous fluid through the formations is intended to displace hydrocarbons contained therein and drive them to one or more producing wells. However, the aqueous displacement fluid often flows through the most permeable zones whereby less permeable zones containing hydrocarbons are bypassed. This uneven flow of the aqueous displacement fluid through the formations or zones reduces the overall yield of hydrocarbons. In any of the foregoing situations, it may be desirable to create a barrier to the flow of injected or natural drive fluid, e.g., aqueous or gas drive fluid, through high permeability channels and fractures in a subterranean formation. These methods are sometimes referred to in the art as “conformance control.”
Another problem that may be encountered during subterranean operations is that treatment fluids introduced to a subterranean formation for the purpose of treating a portion of the subterranean formation may flow away from the zone that was intended to be treated via depleted zones, zones of relatively low pressure, naturally occurring fractures, weak zones having fracture gradients exceeded by the hydrostatic pressure of the drilling fluid, and so forth. As a result, the services provided by the treatment fluids are more difficult to achieve. Barriers to fluid flow through permeable zones of a subterranean formation may be desirable to prevent such a fluid loss.
An approach to preventing the unwanted movement of a fluid through a permeable zone of a subterranean formation has been to introduce a mixture of reagents, initially low in viscosity, into the zone of the formation that has high permeability. After a period of time sufficient to allow the mixture to be pumped into the subterranean formation, or when the mixture is exposed to the elevated temperature of the formation, the mixture of reagents may form a gel to at least partially block the flow of drive fluid. Some known techniques have involved injecting aqueous solutions of polymers and/or polymers with gelling agents into high permeability flow paths of a subterranean formation whereby the polymers are gelled and cross-linked therein. For example, water soluble polymers including copolymers of acrylamide and acrylic acid cross-linked with transition metal ions have been utilized heretofore. However, the use of resin and/or polymer conformance materials may not be economical in all applications. In addition, the use of some resins and/or polymers may raise environmental concerns.
An alternative method of reducing the movement of fluids through permeable zones of a subterranean formation has involved contacting a soap component with a salt to form a precipitate that serves as an at least partial barrier to fluid flow. The precipitates that form as a result of the interaction of a soap component and a salt may be substantially water insoluble. One obstacle that has frequently been encountered when using precipitates formed in this way is that soap components are typically regarded as water insoluble. Thus, different methods have been used to at least partially dissolve a soap component so that it may be introduced into a well bore and interact with a salt therein. One way in which soap components have been dissolved has been through the use of a non-aqueous solvent which is capable of dissolving a selected soap component. Another way in which soap components have been dissolved is to select soap components with relatively high solubility in an aqueous fluid, e.g., α-branched carboxylic acids.
One conventional way of creating a precipitate from a soap component that has been at least partially dissolved and a salt solution has been to sequentially inject the at least partially dissolved soap component and a salt solution. These injections are commonly separated by an injection of a spacer fluid into the well bore. As used herein, “spacer” is defined as a fluid that prevents the soap component and the salt solution from interacting as they pass down the well bore and that is relatively inert with respect to the soap component and the salt solution. One drawback of sequentially injecting the soap component and the salt solution is the expense and time involved in pumping three separate substances downhole.
Another method that has been used to create a fluid diversion barrier is the injection of a treatment fluid comprising micelles that viscosify the treatment fluid, e.g., cause the treatment fluid form a gel. At a high level of viscosity, the treatment fluid may act as a fluid diversion barrier, diverting other treatment fluids away from high permeability zones. In some cases, additives comprising soap components have been included in treatment fluids to, inter alia, maintain the stability and/or viscosity of treatment fluids, particularly at temperatures above about 200° F., and to reduce the amount of the treatment fluid that is lost to the formation as filtrate.